This invention relates to a mechanism for orienting a rotary member such as turn table, etc. in a predetermined angular position.
In a machine tool construction it is frequently necessary for accurately positioning a turn table in a predetermined angularly oriented position. This accurate positioning is needed for variety of purposes. For example, when effecting a turning work and a drilling work in a row, the accurate angular positioning of the turn table is required in an automatic operation.
To attain an accurate angular positioning of the turn table, it is desirable to employ a separate servo drive in addition to a main drive. To this end, a separate servo drive is provided solely for effecting the angular positioning of the turn table. An independent drive mechanism is provided for rotating the turn table in a work operation and this independent drive mechanism is rendered inoperative when the positioning movement is being effected by the servo drive.
U.S. Pat. No. 3,483,767 discloses such a separate servo drive mechanism for accurately positioning a rotary spindle; but this prior art device is disadvantageous in that it takes a relatively long time for angularly orienting the rotary spindle in a predetermined angular position.
Japanese Laid-Open Patent Publication No. 53-95379 discloses another prior art which employs two detectors, i.e. a rough detector and a fine detector. This prior art device can shorten the time required for angularly indexing the rotary member, but a control system thereof becomes very complicated.